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Hubble Spies Massive Star Clusters Near Galactic Core

Date:

September 17, 1999

Source:

Space Telescope Science Institute

Summary:

Penetrating 25,000 light-years of obscuring dust and myriad stars,
NASA's Hubble Space Telescope has provided the clearest view yet of a
pair of the largest young clusters of stars inside our Milky Way galaxy.

Penetrating 25,000 light-years of obscuring dust and myriad stars,NASA's Hubble Space Telescope has provided the clearest view yet of a pair of the largest young clusters of stars inside our Milky Way galaxy.

Located less than 100 light-years from the very center of the Galaxy, these giant clusters have a remarkable excess of massive stars and offer new clues as to how such monumental clusters form.

The Hubble images reinforce the emerging view that the galactic core is a unique place in the Galaxy, where conditions under which stars form are completely different from elsewhere in the Galaxy. The core is a site of ongoing violent star formation, as clouds of molecular hydrogen laced with dust zip around the center of our galaxy like wayward comets. A fireworks show of star birth ignites when the clouds collide.

Called the Arches and Quintuplet clusters, they are 2 and 4 million years old, respectively. The older cluster is more dispersed, and it has stars on the verge of blowing up as supernovae, such as the Pistol Star. The Pistol Star is the brightest star in the Galaxy and was also imaged by Hubble in 1997. Both clusters are destined to be ripped apart in just a few million years by gravitational tidal forces in the Galaxy's core. But in the brief time they are around, they shine more brightly than any other star cluster in the Galaxy.

Having an equivalent mass greater than 10,000 stars like our sun, the monster clusters are 10 times heavier (or more massive) than typical young star clusters scattered throughout our Milky Way. The more compact Arches cluster is so dense, over 100,000 of its stars would fill a spherical region in space whose radius is the distance between the Sun and its nearest neighbor, the star AlphaCentauri, 4.3 light-years away.

Only 1 out of every 10,000,000 stars in the Galaxy is as luminous as the bright Arches cluster stars. This suggests that conditions are so extreme at the hot and dynamic hub of our galaxy, massive stars are favored to form. At least a dozen of the stars weigh about 100 times more than our sun.

Both clusters might have formed when two giant clouds, containing dust and molecular hydrogen, had a head-on-collision. This precipitated the birth of thousands of stars. However, warm interstellar temperatures, powerful magnetic fields, and turbulence inside the interstellar gas may have inhibited smaller clumps of hydrogen from falling together to create many stars lower in mass than our sun.

The observations were made by Don Figer of the Space Telescope Science Institute, using Hubble's NICMOS infrared camera. The results will be published in the November 10 issue of The Astrophysical Journal. Figer's co-investigators are Sungsoo S. Kim (University of California, Los Angeles (UCLA), and the Korea Advanced Institute of Space Science and Technology, Korea), Mark Morris (UCLA), Eugene Serabyn (Jet Propulsion Laboratory, Pasadena), R. Michael Rich and Ian S. McLean (UCLA).

Figer next plans to analyze data obtained with a new near-infrared spectrometer, which he helped build for the Keck telescope. The analysis will help determine just how quickly the Arches cluster will evaporate due to tidal forces. Hubble's successor, the Next Generation Space Telescope, scheduled for launch in 2008, will be able to clearly see the fainter stars in the cluster's core, giving astronomers better insight into star-forming conditions in the heart of our galaxy and into whether conditions there allow stars like our sun to form.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.

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